Flame treatment of aluminum



p 4, 1962 D. J. FALCON FLAME TREATMENT OF ALUMINUM Filed April 21. 1958ES BB6 M\ INVENTOR DAV/0 I FALCON BY I W A2415;

ATTORNEY United States Patent C) 3,052,tl14 FLAME TREATMENT OF ALUMINUMDavid J. Falcon, Arnold, Pa., assignor to Aluminum Compauy of America,Pittsburgh, Pa., a corporation of Pennsylvania Filed Apr. 21, 1958, Ser.No. 729,721 7 Claims. (Cl. 29180) This invention relates to the flametreatment of aluminum surfaces, and more particularly to the flametreatment of thin aluminum strip surfaces, especially foil surfaces instrip form, i.e. in continuous lengths. Aluminum, as generally usedherein, embraces both aluminum of various commercial grades and aluminumbase alloys. Thin aluminum strip, as used herein, means aluminum ofsheet-like section less than .015 inch thick and of continuous orindeterminate length. Aluminum foil, as used herein, means aluminum insheet or strip form less than .006 inch thick.

The commercial applications of thin aluminum sheet and foil have beencontinually increasing, and there is a growing market for aluminum inthin strip form, for example in labeling and packaging. Consequently, ithas become necessary to economically render the surfaces of thinaluminum sheet and foil, particularly in asrolled tempers, as free aspossible of surface contaminants. Such surfaces are thereby made Waterwettable, and conventional printing inks, adhesives, plastic films andother coatings will readily adhere thereto.

Copious amounts of oil are commonly employed in the rolling of aluminumsheet and foil, and the aluminum surfaces retain substantial amounts ofresidual rolling oil on and in the natural films of oxide present oneach surface. Consequently, the as-rolled surfaces exhibit poor waterwettabili-ty. Many commonly used printing inks, wash coats andadhesives, for example, exhibit little or no adhesion to an oilyaluminum surface and may be easily stripped or lifted from the surface.In fact, by far the most objectionable contaminants preventing surfaceadhesion are the lubricants used in the strip rolling of thin aluminumsheet and foil. Consequently, it is generally necessary to removeresidual rolling lubricant from the aluminum surface prior to a coatingstep.

It is well known that rolling oil is volatilized or burned off duringthe process of annealing aluminum sheet or foil. However, annealing iscostly and time consuming, and may not sufficiently remove the rollinglubricant from the metal surface to allow the most satisfactoryadherence of coatings. Furthermore, annealing not only alters themechanical properties of the metal, but also may adversely affect thesurface appearance of thin aluminum strip. That is to say, annealingreduces the tensile strength and yield strength of the metal as comparedto metal in the as-rolled temper, and also may dull the metal surface.Annealing may even result in staining of sheet and foil surfaces whenlubricant is retained on the foil in coil convolutions, for example.

In view of the objections and disadvantages of annealing thin aluminumsheet and foil to remove residual lubricant, it is an object of theinvention to remove such lubricant without subjecting the aluminum toannealing.

It is a general object of this invention to provide a process fortreating thin aluminum strip surfaces, particularly surfaces ofaluminumfoil in continuous strip form, to render such surfacessubstantially free of contaminants and thereby improve the receptivityof such surfaces to variouscoatings, including plastic films, adhesives,inks or other protective or decorative matter.

It is a further object to provide a process for treating thin aluminumsheet or foil to remove rolling lubricant from the surface withoutaffecting the mechanical properties of the sheet or foil.

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It is still a further object to provide a process for flame treating asurface of as-rolled aluminum in thin strip for-m, particularly foilstrip, to remove substantially all of the rolling lubricant withoutaffecting the mechanical properties thereof.

Other objects and advantages of the invention will become evident in thefollowing description thereof.

According to the present invention, a thin aluminum strip surface may bemoved through at least one gas flame so as to volatilize residualrolling lubricant from such surface. Heretofore, it has been though thatsuch a treatment wouldbe impractical or would require, or result in,annealing and/or excessive wrinkling of the thin strip, especially foil.However, it has been found that such a flame treatment may be employedto render the aluminum surface water wettable, and is particularlyeffective in the treatment of foil strip. Such treatment therebyimproves the receptivity of the aluminum surface to various coatings,including adhesives, inks, plastic films or other protective ordecorative matter, without annealing or excessive wrinkling.

In the preferred practice of the invention, a thin aluminum strip,preferably aluminum foil in continuous length, is surface treated byimpinging a gas flame on the surface thereof while subjecting theopposite surface of the moving strip to cooling, for example, by passingthe strip over a relatively cool heat conducting surf-ace. By thisprocedure, substantially all of the residual rolling lubricant isvolatilized from the flame treated surface of the foil strip, and thatsurface is characterized by having water-wettabili-ty at leastsubstantially equal to that of a corresponding annealed strip. The thinstrip may be any as-rolled temper, whether full hard or intermediate.Yet when it is flame treated as described herein, there is nosubstantial loss in mechanical properties resulting from the flametreatment. This has been established by substantially identical tensilestrengths, yield strengths and percent elongations obtained on samplesof foil, before and after such flame treatment. In addition, it is alsopossible to flame treat the foil side of a foil-paper laminate withoutdamagnig the paper laminate. The flame treated foil surface, being waterwettable, is highly receptive to such conventional printing inks asgravure, offset and water base inks, as well as to emulsion typeadhesives, and to nitrocellulose and dewaxed shellac wash coating-s. Infact, the flame treated foil retains good receptivity to a variety ofcoatings. even after storage.

The drawing diagrammatically illustrates apparatus suitable for carryingout the invention in the treatment of a continuous strip of thinaluminum sheet or foil.

Referring to the drawing, a strip 2 of aluminum foil is shown beingcontinuously drawn in the direction indicated by the arrows from anunwind reel 6, over an idler roll 8, and around a relatively cool drum10, exposing one surface of strip 2 to a flame 14 to be furtherdiscussed. The opposite surface of strip 2 is preferably exposed to asecond flame 18 as it is drawn around a second cool drum 12. The flametreated strip is finally taken up on rewind reel 22 and stored forsubsequent use. However, instead of being rewound on reel 22, the strip2 may be drawn directly into another apparatus, not shown in thedrawing, for a coating or other operation.

As the continuously drawn strip 22 moves arcuately in contact with thecool drum 10, gas flame 14 from a burner 16 is impinged on the surfaceof the foil. In like manner, as illustrated in the drawing, the reverseside of the strip is simultaneously treated by flame 18 from a burner 20as it moves arcuately in contact with cool drum 12, so that both sidesof the strip are treated. Generally, as when the aluminum foil issupplied from a coil and rewound into a coil, it will be desirable toflame treat both surfaces of the metal, to avoid re-contamination of thetreated surface by contact with the untreated surface. On the otherhand, it may be quite satisfactory to flame treat only one side of thestrip, as in the case when the metal is fed directly to a coatingapparatus. In such case the second cool drum 12 and burner 20 may beomitted.

During operation, the gas flame 14 or 18 would contact the strip. Theburner 16 or 20 may be located quite close to the strip, say about A; to1% inches. The flame may be generated by burning a gas, such as naturalgas or propane, mixed with air in a burner suitable for the same. Eachburner is preferably a low pressure burner, and is preferably in theform of an elongated manifold substantially the width of the metal stripto be treated. In this manner, the flame treatment is made uniformlyeffective over the strip width. In some cases, more than one such burnermay be employed around each cool drum, so that only one pass through theflame treating apparatus need be made.

The drum or 12 may be cooled by any suitable means, for instance, bycontinuously passing water therethrough. Each drum preferably ismaintained at a temperature below about 212 F. By properly adjusting thedrum temperature, the burner spacing between the burner face and thesurface of the foil, the burner location relative to the point where thestrip leaves the cool drum, and the strip speed and tension, wrinklingmay be substantially avoided and moisture condensation may be minimizedwhile concurrently obtaining the high efficiency in oil removal. Despitethe direct impingement of a flame upon such thin aluminum strip asconventional packaging foils, wrinkling is best avoided when the cooldrum is employed and maintained at a temperature below about 165 F.,although higher temperatures may be employed where thicker strip istreated or when some wrinkling can be tolerated. The flame may beapplied near the point at which the strip leaves the drum, as this alsoappears to minimize wrinkling in the case of foil strip.

The duration of the flame treatment, necessary for obtaining a surfacecompatible with inks and other coatings, is dependent upon thetemperature of the flame, variations in the oil film, the linear speedof the strip and its thickness. Therefore, it may be desirable undersome conditions, to prolong the flame treatment or to provide for aplurality of gas burners around the cool drums. In each case, optimumconditions for yielding a surface highly receptive to printable matterand other coatings may be readily determined through simpleexperimentation.

The following example is given by Way of illustration. As-rolledaluminum foil of 99.45% purity and .00035 inch thick was flame treatedin strip form on each side with a propane-air flame. Two adjacentelongated manifold type burners were provided for each surface of thefoil, and the distance from each burner face to the foil surface was A;of an inch. The cool drum temperature did not exceed approximately 190F. The linear speed of the foil Was 250 feet per minute. The treatedfoil surface exhibited good water Wettabili-ty even when treated withflame from only one burner per surface. Foil treated with two burnersper surface retained good water wettability after several weeks of agingat room temperature. In intermediate tests such foil had retained goodadhesion with ink after two months of aging at room temperature, andafter two weeks of aging at 140 F. had retained good adhesion withnitrocellulose adhesive. There was substantially no change in tensilestrength, yield strength, and percent elongation between a treated anduntreated sample. Similar flame treatments have been effectively carriedout with thin aluminum strips of various other gauges and with variousoperating conditions.

The flame treating process should have extensive use in the packagingtrade where it is necessary to print or otherwise decorate an aluminumfoil overwrap. Remov ing the rolling lubricant by annealing dulls thefoil sur= face. On the other hand, flame treating as rolled foil toimprove its ink adhesion will not materially alter its metallic luster.Therefore, a package, carton, or Wrapper made from as-rolled foil whichhas been flame treated for ink receptivity will be more attractivebecause of its bright surface.

The dead fold characteristics of annealed foil result in a markedtendency for such foil to retain the convolutions imparted to it. Thismay cause problems in feeding sheeted foil or foil laminate to sheet fedprinting presses with resulting excess downtime of the press and slowoperating speeds. These problems are obviated with the use of aluminumfoil in an as-rolled temper having snap-back characteristics. Thus, itis possible to print directly onto a flame treated hard foil surfacewith no paper backing or with merely a laminate of a light paper stock.

As-rolled foil which has been surface conditioned may be used as alithoplate in lithographic printing. Such as-rolled foil also may beused in honeycomb panel as semblies, such as are employed in airplanes,and which must be free from the rolling lubricant before adjoining thevarious parts with organic adhesives. Other uses for flame treated foilin as-rolled tempers will, of course, be obvious to those skilled in theart.

Having thus described my invention, what I claim is:

1. A method for removing residual rolling lubricant from a thin aluminumstrip surface which comprises moving a surface of an aluminum strip lessthan .015 inch thick and in an as-rolled temper through at least one gasflame, while subjecting the surface opposite the flame to cooling, andthereby volatilizing residual rolling lubricant from said flame treatedsurface, whereby said flame treated surface is rendered water wettablewithout substantially affecting the mechanical properties of saidaluminum strip.

2. A method according to claim 1 wherein the gas flame impinges on saidfirst surface as the opposite surface of said strip passes over arelatively cool heat conducting surface.

3. A method according to claim 2 wherein the heat conducting surface ismaintained at a temperature below about 212 F.

4. An aluminum strip less than .015 inch thick and in substantially anas-rolled temper, having at least one surface from which substantiallyall of the residual rolling lubricant has been removed by the flametreatment method of claim 1, and characterized by having freedom fromresidual rolling lubricant and waterwettability of the flame treatedsurface at least substantially equal to that of a corresponding annealedstrip surface, but with mechanical properties of the flame treated stripat least substantially equal to those of the as-rolled strip beforebeing so treated.

5. A method for treating a bright surface of aluminum foil strip in Billas-rolled temper and retaining residual rolling lubricant, whichcomprises impinging a gas flame on said surface as the surface of saidfoil strip opposite the flame passes continuously and arcuately incontact with a relatively cool heat conducting surface, and therebyvolatilizing substantially all of the residual rolling lulbricant fromsaid flame treated surface, whereby said flame treated surface remainsbright and is rendered water wettable without substantial wrinkling ofsaid foil strip and without substantially affecting the mechanicalproperties of said foil strip.

6. A substantially unwrinkled aluminum foil strip in substantially anas-nolled temper, having at least one bright surface from whichsubstantially all of the residual rolling lubricant has been removed bythe flame treatment method of claim 5, and characterized by havingfreedom from residual rolling lubricant, water-wettability and brightappearance of the flame treated surface at least substantially equal tothat of a corresponding annealed foil strip surface, [but withmechanical properties and freedom from wrinkling of the flame treatedfoil strip at least substantially equal to that of the as-rolled foilstrip before being so treated.

7. A method for removing residual rolling lubricant from an aluminumfoil strip surface which comprises moving a first surface of said foilstrip in an as-rolled temper through at least one gas flame whichimpinges on said first surface, while subjecting the surface oppositethe flame to cooling, as it moves arcuately in contact with a heatconducting surface which is maintained at temperature below about 165F., and thereby volatilizing residual rolling lubricant from said first,flame treated surface, whereby said first, flame treated surface isrendered water wettable without substantially afiecting the mechanicalproperties of said aluminum foil strip.

References (Iited in the file of this patent UNITED STATES PATENTS998,900 Hodgson July 25, 1911 1,339,710 Page May 11, 1920 1,864,257Purser June 21, 1932 2,189,836 Schon Feb. 13, 1940 2,295,701 WagnerSept. 15, 1942 2,480,455 Eichner Aug. 30, 1949 2,506,364 Jarvie May 2,1950 OTHER REFERENCES Edwards Frary: Aluminum Industry, vol. 2, 1930.

5. A METHOD FOR TREATING A BRIGHT SURFACE OF ALUMINUM FOIL STRIP IN ANAS-ROLLED TEMPER AND RETAINING RESIDUAL ROLLING LUBRICANT, WHICHCOMPRISES IMPINGING A GAS FLAME ON SAID SURFACE AS THE SURFACE OF SAIDFOIL STRIP OPPOSITE THE FLAME PASSES CONTINOUSLY AND ARCUATELY INCONTACT WITH A RELATIVELY COOL HEAT CONDUCTING SURFACE, AND THEREBYVOLATILIZING SUBSTANTIALLY ALL OF THE RESIDUAL ROLLING